The fate of mesenchymal stem cells transplanted into immunocompetent neonatal mice: implications for skeletal gene therapy via stem cells

Non-clinical assessment of safety, biodistribution and tumorigenicity of human mesenchymal stromal cells

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Good safety profile of mesenchymal stromal cells (MSCs) without toxicity findings.

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MSC biodistribution showed primary distribution to the lung and short persistence.

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No tumor formation observed after 6 months of repeated MSC dosing.

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qPCR and in situ hybridization were combined for the detection of MSCs.

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Data allow progression into clinical trials for acute Graft-versus-Host disease.

Guidelines regulating the development of advanced therapy medicinal products (ATMPs) request nonclinical data for toxicity, biodistribution and tumorigenicity before mesenchymal stromal cell (MSC) products can be administered in large clinical trials. We assessed the biodistribution/persistence, safety and tumorigenicity of MC0518, a human allogeneic MSC product from pooled bone marrow mononuclear cells of eight healthy, adult, unrelated donors, which is currently investigated for the treatment of steroid-refractory acute Graft-versus-Host Disease (aGvHD) after hematopoietic stem cell transplantation. In our GLP studies, immuno-deficient mice were administered repeat doses of MC0518 (once weekly for 6 weeks, i.v.) at doses exceeding the proposed human clinical dose 20-60-fold. No signs of toxicity were observed in the combined biodistribution/toxicity study. Human MSCs in mouse tissues were detected by quantitative PCR (qPCR) and in situ hybridization (ISH). MC0518 showed initial trapping in the lung, occasional distribution into other organs and low tissue persistence beyond 24 h after application. No MSC-induced tumors of human origin were identified after a follow-up of six months. Additionally, we found that the combination of different detection methods (qPCR and ISH) is crucial for a reliable interpretation of biodistribution results. Our data suggest that MC0518 is safe for use in human.

Hematopoietic stem cell-derived functional osteoblasts exhibit therapeutic efficacy in a murine model of osteogenesis imperfecta

Currently, there is no cure for osteogenesis imperfecta (OI)-a debilitating pediatric skeletal dysplasia. Herein we show that hematopoietic stem cell (HSC) therapy holds promise in treating OI. Using single-cell HSC transplantation in lethally irradiated oim/oim mice, we demonstrate significant improvements in bone morphometric, mechanics, and turnover parameters. Importantly, we highlight that HSCs cause these improvements due to their unique property of differentiating into osteoblasts/osteocytes, depositing normal collagen-an attribute thus far assigned only to mesenchymal stem/stromal cells. To confirm HSC plasticity, lineage tracing was done by transplanting oim/oim with HSCs from two specific transgenic mice-VavR, in which all hematopoietic cells are GFP+ and pOBCol2.3GFP, where GFP is expressed only in osteoblasts/osteocytes. In both models, transplanted oim/oim mice demonstrated GFP+ HSC-derived osteoblasts/osteocytes in bones. These studies unequivocally establish that HSCs differentiate into osteoblasts/osteocytes, and HSC transplantation can provide a new translational approach for OI.

Mesenchymal stem/stromal cell-based therapy: mechanism, systemic safety and biodistribution for precision clinical applications

Mesenchymal stem/stromal cells (MSCs) are a promising resource for cell-based therapy because of their high immunomodulation ability, tropism towards inflamed and injured tissues, and their easy access and isolation. Currently, there are more than 1200 registered MSC clinical trials globally. However, a lack of standardized methods to characterize cell safety, efficacy, and biodistribution dramatically hinders the progress of MSC utility in clinical practice. In this review, we summarize the current state of MSC-based cell therapy, focusing on the systemic safety and biodistribution of MSCs. MSC-associated risks of tumor initiation and promotion and the underlying mechanisms of these risks are discussed. In addition, MSC biodistribution methodology and the pharmacokinetics and pharmacodynamics of cell therapies are addressed. Better understanding of the systemic safety and biodistribution of MSCs will facilitate future clinical applications of precision medicine using stem cells.

Prenatal stem cell therapy for inherited diseases: Past, present, and future treatment strategies

Imagine the profits in quality of life that can be made by treating inherited diseases early in life, maybe even before birth! Immense cost savings can also be made by treating diseases promptly. Hence, prenatal stem cell therapy holds great promise for developing new and early‐stage treatment strategies for several diseases. Successful prenatal stem cell therapy would represent a major step forward in the management of patients with hematological, metabolic, or immunological disorders. However, treatment before birth has several limitations, including ethical issues. In this review, we summarize the past, the present, and the future of prenatal stem cell therapy, which includes an overview of different stem cell types, preclinical studies, and clinical attempts treating various diseases. We also discuss the current challenges and future strategies for prenatal stem cell therapy and also new approaches, which may lead to advancement in the management of patients with severe incurable diseases.

Dissecting the Pharmacodynamics and Pharmacokinetics of MSCs to Overcome Limitations in Their Clinical Translation

Recently, mesenchymal stromal stem cells (MSCs) have been proposed as therapeutic agents because of their promising preclinical features and good safety profile. However, their introduction into clinical practice has been associated with a suboptimal therapeutic profile. In this review, we address the biodistribution of MSCs in preclinical studies with a focus on the current understanding of the pharmacodynamics (PD) and pharmacokinetics (PK) of MSCs as key aspects to overcome unsatisfactory clinical benefits of MSC application. Beginning with evidence of MSC biodistribution and highlighting PK and PD factors, a new PK-PD model is also proposed. According to this theory, MSCs and their released factors are key players in PK, and the efficacy biomarkers are considered relevant for PD in more predictive preclinical investigations. Accounting for the PK-PD relationship in MSC translational research and proposing new models combined with better biodistribution studies could allow realization of the promise of more robust MSC clinical translation.

Mesenchymal stromal cells' role in tumor microenvironment: involvement of signaling pathways

Mesenchymal stromal cells (MSCs) are adult multipotent stem cells residing as pericytes in various tissues and organs where they can differentiate into specialized cells to replace dying cells and damaged tissues. These cells are commonly found at injury sites and in tumors that are known to behave like " wounds that do not heal." In this article, we discuss the mechanisms of MSCs in migrating, homing, and repairing injured tissues. We also review a number of reports showing that tumor microenvironment triggers plasticity mechanisms in MSCs to induce malignant neoplastic tissue formation, maintenance, and chemoresistance, as well as tumor growth. The antitumor properties and therapeutic potential of MSCs are also discussed.

Engraftability of Murine Bone Marrow-Derived Multipotent Mesenchymal Stem Cell Subpopulations in the Tissues of Developing Mice following Systemic Transplantation

INTRODUCTION

Cell therapies for generalized musculoskeletal diseases would require distribution of cells to all the skeletal tissues; however, there are controversies regarding the transplantability of multipotent mesenchymal stems cells (MSCs). We generated single-cell subpopulations of MSCs from murine bone marrow and assessed them for differences in trafficking through the circulatory system and engraftment in bone and other tissues.

MATERIALS AND METHODS

Seven single-cell clonal subpopulations were generated by serial dilution of GFP-marked MSCs isolated from bone marrow. The subpopulations were examined for putative MSC surface marker expression, in vitro differentiation toward osteogenic and adipogenic lineages, migration and engraftment in different tissues following intravenous delivery in normal, sublethally irradiated neonatal mice.

RESULTS

The surface marker expression profile revealed notable differences among clonal cells, specifically CD44 and CD105. All the cell subpopulations differentiated toward osteogenic and adipogenic lineages, with some committed to only one or the other. Two clones enriched in CXCR4 expression were highly efficient in migrating and engrafting in skeletal tissue including bone; this confirmed the role of this chemokine in cell migration. Donor cells retrieved from various tissues displayed different morphologies and potential differentiation into tissue cell type of engraftment, suggesting modification by the tissues in which the donor cells engrafted.

CONCLUSION

We have reported that, within bone marrow, there are heterogeneous subpopulations of MSCs that may differ in their ability to migrate in the circulatory system and engraft in different tissues.

Human adipose-derived stromal/stem cells demonstrate short-lived persistence after implantation in both an immunocompetent and an immunocompromised murine model

Introduction

Mesenchymal cells are emerging as a promising cell platform for regenerative therapies. However, the fate of cells after transplantation in many different disease settings and tissue beds remains unclear.

Methods

In this study, human adipose-derived stromal/stem (ASCs) cells were fluorescently labeled with a membrane dye and injected into both immunocompetent and immunocompromised mouse strains. Cells were injected either as single cell suspensions, or as self-assembling spheroids. In parallel, cells were purposefully devitalized prior to injection and then implanted in the opposite side in a randomized fashion. These ‘control’ groups were included to determine whether the fluorescent membrane dye would remain localized at the injection site despite the use of nonviable cells. Cell implants and the surrounding tissues were harvested on days 3, 10 and 21 after in vivo delivery and evaluated in a blinded manner. Injection sites were analyzed by fluorescent microscopy, and human cell numbers were quantified using PCR detection of a human-specific endogenous retrovirus (ERV-3). Host response was evaluated by immunofluorescent staining of macrophages.

Results

ERV-3 quantification showed that 95% of the human cells that were viable when they were injected were undetectable at the three-week time-point. Although fluorescent signal persisted for the entire study period, further analysis revealed that much of this signal was located within host macrophages.

Conclusions

These results suggest that human ASCs survive for less than three weeks after injection into even immunocompromised mice, and call into question the notion that human ASCs are immuno-privileged and capable of surviving for extended periods in xenogeneic and/or allogeneic models.

Pre- and postnatal transplantation of fetal mesenchymal stem cells in osteogenesis imperfecta: a two-center experience

Osteogenesis imperfecta (OI) can be recognized prenatally with ultrasound. Transplantation of mesenchymal stem cells (MSCs) has the potential to ameliorate skeletal damage. We report the clinical course of two patients with OI who received prenatal human fetal MSC (hfMSC) transplantation and postnatal boosting with same-donor MSCs. We have previously reported on prenatal transplantation for OI type III. This patient was retransplanted with 2.8 × 10(6) same-donor MSCs per kilogram at 8 years of age, resulting in low-level engraftment in bone and improved linear growth, mobility, and fracture incidence. An infant with an identical mutation who did not receive MSC therapy succumbed at 5 months despite postnatal bisphosphonate therapy. A second fetus with OI type IV was also transplanted with 30 × 10(6) hfMSCs per kilogram at 31 weeks of gestation and did not suffer any new fractures for the remainder of the pregnancy or during infancy. The patient followed her normal growth velocity until 13 months of age, at which time longitudinal length plateaued. A postnatal infusion of 10 × 10(6) MSCs per kilogram from the same donor was performed at 19 months of age, resulting in resumption of her growth trajectory. Neither patient demonstrated alloreactivity toward the donor hfMSCs or manifested any evidence of toxicities after transplantation. Our findings suggest that prenatal transplantation of allogeneic hfMSCs in OI appears safe and is of likely clinical benefit and that retransplantation with same-donor cells is feasible. However, the limited experience to date means that it is not possible to be conclusive and that further studies are required.

Differentiating multipotent mesenchymal stromal cells generate factors that exert paracrine activities on exogenous MSCs: Implications for paracrine activities in bone regeneration

The mechanisms by which multipotent mesenchymal stromal cells (MSCs) contribute to tissue repair following transplantation into host tissues remains poorly understood. Current concepts suggest that, in addition to differentiation into cells of the host tissues, MSCs also generate trophic factors that modulate host tissue microenvironment to aid in the repair process. In this communication, we assessed whether factors secreted by MSCs undergoing osteogenic differentiation induce expression of osteoblast markers in exogenous MSCs as well as their migration. Murine MSCs were cultured in osteogenic medium, and at different time points, medium conditioned by the cells was collected and assessed for its effects on differentiation and migration of exogenous MSCs. In addition, we determined whether MSCs infused into mice femurs expressed genes encoding for factors predicted to play a role in paracrine activities. The results showed that MSCs maintained in osteogenic medium, secreted factors at specific time points that induced alkaline phosphatase activity (ALP) in exogenous MSCs as well as their migration. MSCs infused into mice femurs and retrieved at different days expressed genes that encoded predicted factors that play a role in cell differentiation and migration. Neutralizing antibodies to bone morphogenetic protein-2 (BMP-2) led to the decrease in ALP activity by exogenous MSCs. These data demonstrated that, as MSCs differentiate toward osteogenic lineage, they secrete factors that induce recruitment and differentiation of endogenous progenitors. These data reveal mechanisms by which donor MSCs may contribute to the bone reparative process and provide a platform for designing approaches for stem cell therapies of musculoskeletal disorders.

Comparison of the characteristics of mesenchymal stem cells obtained from prostate tumors and from bone marrow cultured in conditioned medium

Prostate cancer (PCa) is the most common type of cancer worldwide. Mesenchymal stem cells (MSCs) can also be utilized as ‘tumor stromal cells’, which are associated with invasive and metastatic malignant tumor cells. Our study aimed to investigate MSCs in prostate tumors and normal MSCs and evaluate their differential characteristics. Normal MSCs (BMMSCs) were isolated from the femur and tibia of normal mice; prostate tumor MSCs (PCa-MSCs) were obtained from prostate tumors implanted in mice. These two types of MSCs were induced to differentiate into adipocytes, bone cells and chondrocytes. Growth curves were used to analyze the growth ability of PCa-MSCs and BMMSCs. Tritium-labeled thymidine (3H-TdR) was used to evaluate cell proliferation of RM-1 stimulated by MSCs. The time taken for PCa-MSCs to reach 90% confluence was markedly shorter than that of BMMSCs (8–10 vs. 12–14 days). The differentiation ability of PCa-MSCs was similar to that described in previous reports. The growth ability of PCa-MSCs was significantly higher than that of BMMSCs. The proliferative activity of PCa-MSCs was also higher than that of BMMSCs. Our data showed that PCa-MSCs exhibit identical characteristics when compared with those of MSCs. Additionally, their proliferative activity and growth ability were significantly higher when compared with these values in BMMSCs, which appear to have an intrinsic, cell-specific capacity to localize to PCa. The possible role of PCa-MSCs in the process of PCa development requires further clarification.

Long-term in-vivo tumorigenic assessment of human culture-expanded adipose stromal/stem cells

After more than a decade of extensive experimentation, the promise of stem cells to revolutionize the field of medicine has negotiated their entry into clinical trial. Adipose tissue specifically holds potential as an attainable and abundant source of stem cells. Currently undergoing investigation are adipose stem cell (ASC) therapies for diabetes and critical limb ischemia, among others. In the enthusiastic pursuit of regenerative therapies, however, questions remain regarding ASC persistence and migration, and, importantly, their safety and potential for neoplasia. To date, assays of in vivo ASC activity have been limited by early end points. We hypothesized that with time, ASCs injected subcutaneously undergo removal by normal tissue turnover and homeostasis, and by the host's immune system. In this study, a high dose of culture expanded ASCs was formulated and implanted as multicellular aggregates into immunocompromised mice, which were maintained for over one year. Animals were monitored for toxicity, and surviving cells quantified at study endpoint. No difference in growth/weight or lifespan was found between cell-treated and vehicle treated animals, and no malignancies were detected in treated animals. Moreover, real-time PCR for a human specific sequence, ERV-3, detected no persistent ASCs. With the advent of clinical application, clarification of currently enigmatic stem cell properties has become imperative. Our study represents the longest duration determination of stem cell activity in vivo, and contributes strong evidence in support of the safety of adipose derived stem cell applications.

Optimization of genetic engineering and homologous recombination of collagen type I genes in rat bone marrow mesenchymal stem cells (MSC)

Mutations in COL1A1 or COL1A2 genes lead to osteogenesis Imperfecta (OI) in humans. There are three possiblities to successfully treat OI including (1) gene therapy, (2) mesenchymal stem cell (MSC) therapy, or (3) a combination of both. The aim of this study was to develop a model for combined gene/cell OI therapy by targeting Col1a1 and Col1a2 genes with isogenic sequences from corresponding human genes in rat bone marrow (BM)-derived MSCs. The recombination efficacy was tested for five different rat-human-rat hybrid DNAs with rat fragments that were 1 to 4 kb long. For selection of transfected clones a neomycine resistance gene was cotransfected, and clones resistant to G418 (G418(+)) were recovered and screened for integration of specific gene loci in the rat genome. Over 90% of G418(+) clones correctly integrated the rat-human-rat hybrid DNAs, and both OI loci in the rat genome were targeted to a similar degree. Longer homologous sequences integrated into rat collagen genes approximately 10 times more efficiently. Based on our data the nonviral gene targeting technology could be potentially employed to repair collagen genes in OI patients.

Bone marrow stromal cells contribute to bone formation following infusion into femoral cavities of a mouse model of osteogenesis imperfecta

Currently, there are conflicting data in literature regarding contribution of bone marrow stromal cells (BMSCs) to bone formation when the cells are systemically delivered in recipient animals. To understand if BMSCs contribute to bone cell phenotype and bone formation in osteogenesis imperfecta bones (OI), MSCs marked with GFP were directly infused into the femurs of a mouse model of OI (oim). The contribution of the cells to the cell phenotype and bone formation was assessed by histology, immunohistochemistry and biomechanical loading of recipient bones. Two weeks following infusion of BMSCs, histological examination of the recipient femurs demonstrated presence of new bone when compared to femurs injected with saline which showed little or no bone formation. The new bone contained few donor cells as demonstrated by GFP fluorescence. At 6 weeks following cell injection, new bone was still detectable in the recipient femurs but was enhanced by injection of the cells suspended in pepsin solubilized type I collagen. Immunofluorescence and immunohistochemical staining showed that donor GFP positive cells in the new bone were localized with osteocalcin expressing cells suggesting that the cells differentiated into osteoblasts in vivo. Biomechanical loading to failure in three point bending, revealed that, femurs infused with BMSCs in PBS or in soluble type I collagen were biomechanically stronger than those injected with PBS or type I collagen alone. Taken together, the results indicate that transplanted cells differentiated into osteoblasts in vivo and contributed to bone formation in vivo; we also speculate that donor cells induced differentiation or recruitment of endogenous cells to initiate reparative process at early stages following transplantation.

Genetically engineered mesenchymal stem cells: The ongoing research for bone tissue engineering

Bone grafting is crucial in the surgical treatment of bone defects and nonunion fractures. Autogenous bone, allogenous bone, and biomaterial scaffold are three main sources of bone grafts. The biomaterial scaffold, both natural and synthetic, is widely accessible but weak in osteogenic potential. One approach to solve this problem is cell-based bone tissue engineering (BTE), established by growing living osteogenic cells on scaffold in vitro to build up its osteoinducitive capability. Mesenchymal stem cell (MSC) is suitable for use in cell-based BTE, but it remains a considerable challenge to induce MSCs to form solely bone and while preventing MSCs from differentiating into fats, muscles, and possibly neural elements in vivo. Recently, there is a drastic rise in use of genetically engineered MSCs, which can secrete growth factors or alter the transcription level, leading to osteoblast lineage commitment, bone formation, fracture repair, and spinal fusion. In this article, we reviewed the literatures regarding applications of genetically engineered MSCs in BTE. We addressed the currently applicable genes and candidate genes for MSCs modification, transduction efficiency and safety issues of the transfect vectors, and administration routes, and we briefly described in vivo tracking and potential clinical application of the genetically modified MSCs in BTE.

Orthopedic gene therapy in 2008

Orthopedic disorders, although rarely fatal, are the leading cause of morbidity and impose a huge socioeconomic burden. Their prevalence will increase dramatically as populations age and gain weight. Many orthopedic conditions are difficult to treat by conventional means; however, they are good candidates for gene therapy. Clinical trials have already been initiated for arthritis and the aseptic loosening of prosthetic joints, and the development of bone-healing applications is at an advanced, preclinical stage. Other potential uses include the treatment of Mendelian diseases and orthopedic tumors, as well as the repair and regeneration of cartilage, ligaments, and tendons. Many of these goals should be achievable with existing technologies. The main barriers to clinical application are funding and regulatory issues, which in turn reflect major safety concerns and the opinion, in some quarters, that gene therapy should not be applied to nonlethal, nongenetic diseases. For some indications, advances in nongenetic treatments have also diminished enthusiasm. Nevertheless, the preclinical and early clinical data are impressive and provide considerable optimism that gene therapy will provide straightforward, effective solutions to the clinical management of several common debilitating disorders that are otherwise difficult and expensive to treat.

Potential implications of cell therapy for osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a brittle-bone disease whose hallmark is bone fragility. Since the disease is genetic, there is currently no available cure. Several pharmacological agents have been tried with not much success, except the recent use of bisphosphonates. Stem cells have been suggested as an alternative OI treatment, but many hurdles remain before this technology can be applied for treating patients with OI. This review summarizes what is known at present regarding the application of stem cells to treat OI using animal models, clinical trials using mesenchymal stem cells to treat patients with OI and the knowledge gained from the clinical trials. Application of gene therapy in combination with stem cells is also discussed. The hurdles to be overcome to bring stem cells close to the clinic and future perspectives are discussed.

Distribution of murine adipose-derived mesenchymal stem cells in vivo following transplantation in developing mice

Systemic delivery of mesenchymal stem cells (MSCs) or stromal cells in vivo is attractive because it offers means of disseminating therapeutic cells to various tissues and organs in vivo. In the present study, we investigated the distribution and engraftment of the murine adipose-derived mesenchymal stem cells (ADSCs) without exposure to or exposed to bone microenvironment or transforming growth factor-beta1 (TGF-beta1) prior to transplantation into developing mice. The ADSCs harvested from the murine inguinal fat pad exhibited potential for differentiation toward osteogenic and adipogenic cell lineages in vitro. Fourteen days after systemic transplantation of the ADSCs marked with enhanced green fluorescent protein (EGFP) into developing mice, minimal donor GFP(+) cells were detected in the skeletal tissues in a limited number of the recipient mice. Exposure of the ADSCs to bone microenvironment for 7 or 14 days prior to transplantation into developing mice enhanced their migration and survival in the bones of the recipient mice. Exposure of ADSCs to TGF-beta1 prior to systemic transplantation exerted similar effects on cell migration and engraftment in various tissues, including the bones of the recipient developing mice. At 28 days following systemic transplantation, the ADSCs exposed to bone microenvironment were restricted mostly to the skeletal tissues of the recipient mice. Donor cells retrieved from the bones of the recipient mice at 28 days following cell transplantation expressed the differentiation markers Runx2 and Osterix (Osx). These data suggest that exposure of ADSCs to bone microenvironment or to TGF-beta1 prior to transplantation enhances their survival in the skeletal tissues following transplantation.

In vivo Differentiation Potential of Mesenchymal Stem Cells: Prenatal and Postnatal Model Systems

SUMMARY: Most of our knowledge of mesenchymal stem cell (MSC) biology is derived from in vitro systems that are often highly contrived to favor culture expansion or specific differentiation events. However, any conclusions drawn from in vitro studies regarding MSC differentiation capacity, immune properties, or therapeutic potential must be validated by in vivo studies to ultimately be meaningful. At the present time, there are relatively few in vivo studies demonstrating differentiation and functional integration of MSCs into host tissues after transplantation. There is a need for in vivo model systems to assay MSC biology and to move potential therapeutic strategies forward. Here, we review prenatal model systems as potentially advantageous for the in vivo characterization of MSCs, and we critically review the results of in vivo studies of MSC transplantation in prenatal and postnatal model systems with an emphasis on proven engraftment and differentiation.

Pilot study on the interaction between B16 melanoma cell-line and bone-marrow derived mesenchymal stem cells

Bone-marrow derived mesenchymal stem cells (BMSCs) have the potential to differentiate into osteocytes, chondrocytes, adipocytes and endothelial cells. The interaction between BMSCs and epithelial tumor cell was enhanced on proliferation. Our previous study had shown that BMSCs maybe participate in angiogenesis in melanoma in vivo. The aim of this study was to investigate the interaction between B16 melanoma cells and BMSCs in vitro, the mechanism of BMSCs participating in melanoma angiogenesis in vivo is unclear, so a co-culture system containing BMSCs and B16 melanoma cells, based on transwell indirect model, was established, and the interaction between BMSCs and B16 melanoma cells was studied in vitro. In our study, BMSCs were generated out of bone marrow from C57 mouse, isolated BMSCs were positive for the markers CD105, CD90, CD73, CD44 and CD166 and negative for endothelial markers, which acquired endothelial phenotype (including the expression of VEGFR-1, VEGFR-2, Factor VIII) after co-culture with B16 melanoma cells; at the same time, B16 melanoma cells also up-regulated the expression of VEGF-a, VEGFR-1, VEGFR-2 and Factor VIII. The proliferation rate of B16 melanoma cells and BMSCs were also found to be increased. We could show the differentiation of BMSCs into cells with phenotypic features of endothelial cells. BMSCs promoted proliferation of tumor cells and improved the microenvironment in tumor. Our study suggests that the BMSCs may play an important role in tumor angiogenesis.

Concise review: isolation and characterization of cells from human term placenta: outcome of the first international Workshop on Placenta Derived Stem Cells

Placental tissue draws great interest as a source of cells for regenerative medicine because of the phenotypic plasticity of many of the cell types isolated from this tissue. Furthermore, placenta, which is involved in maintaining fetal tolerance, contains cells that display immunomodulatory properties. These two features could prove useful for future cell therapy-based clinical applications. Placental tissue is readily available and easily procured without invasive procedures, and its use does not elicit ethical debate. Numerous reports describing stem cells from different parts of the placenta, using nearly as numerous isolation and characterization procedures, have been published. Considering the complexity of the placenta, an urgent need exists to define, as clearly as possible, the region of origin and methods of isolation of cells derived from this tissue. On March 23-24, 2007, the first international Workshop on Placenta Derived Stem Cells was held in Brescia, Italy. Most of the research published in this area focuses on mesenchymal stromal cells isolated from various parts of the placenta or epithelial cells isolated from amniotic membrane. The aim of this review is to summarize and provide the state of the art of research in this field, addressing aspects such as cell isolation protocols and characteristics of these cells, as well as providing preliminary indications of the possibilities for use of these cells in future clinical applications.

Efficient and rapid osteoinduction in an immune-competent host

Osteoinductive systems to induce targeted rapid bone formation hold clinical promise, but development of technologies for clinical use that must be tested in animal models is often a difficult challenge. We previously demonstrated that implantation of human cells transduced with Ad5F35BMP2 to express high levels of bone morphogenetic protein-2 (BMP2) resulted in rapid bone formation at targeted sites. Inclusion of human cells in this model precluded us from testing this system in an immune-competent animal model, thus limiting information about the efficacy of this approach. Here, for the first time we demonstrate the similarity between BMP2-induced endochondral bone formation in a system using human cells in an immune-incompetent mouse and a murine cell-based BMP2 gene therapy system in immune-competent animals. In both cases the delivery cells are rapidly cleared, within 5 days, and in neither case do they appear to contribute to any of the structures forming in the tissues. Endochondral bone formation progressed through a highly ordered series of stages that were both morphologically and temporally indistinguishable between the two models. Even longterm analysis of the heterotopic bone demonstrated similar bone volumes and the eventual remodeling to form similar structures. The results suggest that the ability of BMP2 to rapidly induce bone formation overrides contributions from either immune status or the nature of delivery cells.

Distribution of single-cell expanded marrow derived progenitors in a developing mouse model of osteogenesis imperfecta following systemic transplantation

We evaluated single-cell-expanded, marrow-derived progenitors for engraftment in a developing mouse model of osteogenesis imperfecta (OI) following systemic transplantation. The present study was initiated to evaluate the potential of mesenchymal stem cells to treat OI. Single-cell-derived progenitors were prepared from marrow stromal cells harvested from normal mice. Selected single-cell-expanded progenitors marked with green fluorescent protein were injected into the neonatal mouse model of OI, and the recipient mice were sacrificed at 2 and 4 weeks following cell transplantation. Examination of the tissues harvested from recipient mice at 2 and 4 weeks after cell transplantation demonstrated that the cells extravasated and engrafted in most of the bones as well as other tissues. Tissue sections made from the tibias and femurs of a selected recipient mouse showed that the cells were distributed in bone marrow, trabecular, and cortical bone as demonstrated by histology and confocal microscopy. The cells that engrafted in the bones of the recipient mouse synthesized and deposited type I collagen composed of alpha1(I) and alpha2(I) collagen heterotrimers. Genotyping and gene expression analysis of the cells retrieved from the bones of the recipient mouse at 2 and 4 weeks demonstrated that the cells expressed osteoblast-specific genes, suggesting that the donor cells differentiated into osteoblasts in vivo with no evidence of cell fusion. These data suggest that progenitors infused in developing mice will engraft in various tissues including bones, undergo differentiation, and deposit matrix and form bone in vivo. Disclosure of potential conflicts of interest is found at the end of this article.

Murine bone marrow stromal progenitor cells elicit an in vivo cellular and humoral alloimmune response

Stromal progenitor cells (SPC) exhibit immunosuppressive effects in vitro that have led to speculation regarding their capacity to evade host immune recognition and to treat autoimmune diseases and gravt-versus-host disease. However, there is little in vivo experimental data to support these immunologic claims. To assess immune recognition of SPC in vivo, we evaluated the immune response of animals transplanted with SPC. C57BL/6 (B6) or Balb/c adult, murine, bone marrow-derived SPC (AmSPC) were administered by intraperitoneal injection into B6 recipients. T cell proliferation and alloantibody response was assessed from spleens and peripheral blood harvested from transplanted animals and analyzed by cell proliferation assay and flow cytometry. To assess tolerance induction, transplanted animals also received allogeneic skin grafts. Animals injected with allogeneic AmSPC mounted an accelerated CD4 response to alloantigen compared to syngeneic AmSPC injected and uninjected controls. Allogeneic AmSPC-injected animals also demonstrated high titers (> or =1:1000) of antibody directed against allogeneic AmSPC targets. Animals primed with donor or host-matched AmSPC also failed to induce tolerance, and all animals exhibited rejection of allogeneic skin grafts (n = 7, P < .0001). In contrast to their in vitro behavior, our data demonstrate that AmSPC are recognized by the host immune system in vivo, elicit a cellular and humoral immune response, and fail to induce tolerance. These findings have significant implications for all allogeneic SPC-based therapeutic strategies.

Widespread distribution and muscle differentiation of human fetal mesenchymal stem cells after intrauterine transplantation in dystrophic mdx mouse

Duchenne muscular dystrophy (DMD) is a common X-linked disease resulting from the absence of dystrophin in muscle. Affected boys suffer from incurable progressive muscle weakness, leading to premature death. Stem cell transplantation may be curative, but is hampered by the need for systemic delivery and immune rejection. To address these barriers to stem cell therapy in DMD, we investigated a fetal-to-fetal transplantation strategy. We investigated intramuscular, intravascular, and intraperitoneal delivery of human fetal mesenchymal stem cells (hfMSCs) into embryonic day (E) 14-16 MF1 mice to determine the most appropriate route for systemic delivery. Intramuscular injections resulted in local engraftment, whereas both intraperitoneal and intravascular delivery led to systemic spread. However, intravascular delivery led to unexpected demise of transplanted mice. Transplantation of hfMSCs into E14-16 mdx mice resulted in widespread long-term engraftment (19 weeks) in multiple organs, with a predilection for muscle compared with nonmuscle tissues (0.71% vs. 0.15%, p < .01), and evidence of myogenic differentiation of hfMSCs in skeletal and myocardial muscle. This is the first report of intrauterine transplantation of ontologically relevant hfMSCs into fully immunocompetent dystrophic fetal mice, with systemic spread across endothelial barriers leading to widespread long-term engraftment in multiple organ compartments. Although the low-level of chimerism achieved is not curative for DMD, this approach may be useful in other severe mesenchymal or enzyme deficiency syndromes, where low-level protein expression may ameliorate disease pathology.

Imaging stem cells implanted in infarcted myocardium

Stem cell-based cellular cardiomyoplasty represents a promising therapy for myocardial infarction. Noninvasive imaging techniques would allow the evaluation of survival, migration, and differentiation status of implanted stem cells in the same subject over time. This review describes methods for cell visualization using several corresponding noninvasive imaging modalities, including magnetic resonance imaging, positron emission tomography, single-photon emission computed tomography, and bioluminescent imaging. Reporter-based cell visualization is compared with direct cell labeling for short- and long-term cell tracking.

Labelling of human adipose-derived stem cells for non-invasive in vivo cell tracking

Human adipose-derived stem cells (ASC) can be expanded in an undifferentiated state or differentiated along the osteogenic, chondrogenic, adipogenic, myogenic, endothelial and neurogenic lineage. To test their in vivo and in situ regenerative potential, their fate needs to be traced after application in suitable defect models. Non-invasive imaging systems allow for real time tracking of labelled cells in the living animal. We have evaluated a bioluminescence cell tracking approach to visualise ASC labelled with luciferase in the living animal. Two procedures have been tested to efficiently label human stem cells with a reporter gene (luciferase, green fluorescent protein), namely lipofection with Lipofectamine 2000 and electroporation with a Nucleofector device. With both lipofection and nucleofection protocols, we have reached transfection efficiencies up to 60%. Reporter gene expression was detectable for 3 weeks in vitro and did not interfere with the phenotype and the stem cell properties of the cells. By means of a highly sensitive CCD camera, we were able to achieve real time imaging of cell fate for at least 20 days after application (intravenous, intramuscular, intraperitoneal, subcutaneous) in nude mice. Moreover, we were able to influence cell mobility by choosing different modes of application such as enclosure in fibrin matrix. The optical imaging system with transient transfection is an elegant cell-tracking concept to follow survival and fate of human stem cells in small animals.

Innate immune response to human bone marrow fibroblastic cell implantation in CB17 scid/beige mice

Immunocompromised mouse models have been extensively used to assess human cell implantation for evaluation of cytotherapy, gene therapy and tissue engineering strategies, as these mice are deficient in T and B lymphoid cells. However, the innate immune response and its effect on human cell xenotransplantation in these mouse models are mainly unknown. The aim of this study is to characterise the myeloid populations in the spleen and blood of CB17 scid beige (CB17 sb) mice, and to study the inflammatory cell responses to xenogeneic implantation of enhanced green fluorescent protein (GFP)-labelled human bone marrow fibroblastic (HBMF) cells into CB17 sb mice. The results indicate that even though CB17 sb mice are deficient in B- and T-cells, they exhibit some increases in their monocyte (Mo), macrophage (Mphi) and neutrophil (Neu) populations. NK cell and eosinophil populations show no differences compared with wild-type Balb/C mice. An innate immune response, identified by CR3 (CD11b/CD18)-positive myeloid inflammatory cells and F4/80-positive macrophages, was evident in the tissues where HBMF cells were implanted. As a consequence, the majority of implanted HBMF cells were eliminated by 4 weeks after implantation. Interestingly, the mineralised matrix formed by osteogenic HBMF cells was also eroded by multinuclear Mphi-like giant cells. We conclude that CB17 sb mice retain active innate immune cells, which respond to HBMF cell xenotransplantation. This study highlights the importance of the innate immune cells in the anti-xenograft response and suggests that strategies to block the activities of these cells may ameliorate the progressive long-term elimination of xenotransplants.

Progenitors systemically transplanted into neonatal mice localize to areas of active bone formation in vivo: implications of cell therapy for skeletal diseases

The potential of cell or gene therapy to treat skeletal diseases was evaluated through analysis of transplanted osteoprogenitors into neonatal homozygous and heterozygous osteogenesis imperfecta mice (oim). The osteoprogenitors used for transplantation were prepared by injection of mesenchymal stem cells (MSCs) marked with the green fluorescent protein (GFP) into normal mice with the subsequent retrieval of the cells at 35 days. The retrieved cells referred to here as osteoprogenitors were expanded in culture and transplanted into the 2-day-old oim mice via the superficial temporal vein. The recipient mice were evaluated at 2 and 4 weeks after cell transplantation. Four weeks after transplantation, tissue sections made from femurs and tibias of oim mice showed that the GFP-positive (GFP(+)) cells were distributed on the surfaces of the bone spicules in the spongiosa, the area of active bone formation. In the diaphysis, the GFP(+) cells were distributed in the bone marrow, on the endosteal surfaces, and also in the cortical bone. Immunofluorescence localization for GFP confirmed that the fluorescence seen in tissue sections was due to the engrafted donor cells, not bone autofluorescence. Gene expression analysis by polymerase chain reaction of the GFP(+) cells retrieved from the bones and marrow of the recipient mice demonstrated that the cells from bone were osteoblasts, whereas those from bone marrow were progenitors. These data demonstrate that MSCs delivered systemically to developing osteogenesis imperfecta mice engraft in bones, localize to areas of active bone formation, differentiate into osteoblasts in vivo, and may contribute to bone formation in vivo.

The 3rd International Meeting on Gene Therapy in Rheumatology and Orthopaedics

The 3rd International Meeting on Gene Therapy in Rheumatology and Orthopaedics was held in Boston, Massachusetts, USA in May 2004. Keystone lectures delivered by Drs Joseph Glorioso and Inder Verma provided comprehensive, up-to-date information on all major virus vectors. Other invited speakers covered the application of gene therapy to treatment of arthritis, including the latest clinical trial in rheumatoid arthritis, as well as lupus and Sjögren's syndrome. Applications in mesenchymal stem cell biology, tissue repair, and regenerative medicine were also addressed. The field has advanced considerably since the previous meeting in this series, and further clinical trials seem likely.

Influence of hypoxia on the domiciliation of mesenchymal stem cells after infusion into rats: possibilities of targeting pulmonary artery remodeling via cells therapies?

BACKGROUND

Bone marrow (BM) cells are promising tools for vascular therapies. Here, we focused on the possibility of targeting the hypoxia-induced pulmonary artery hypertension remodeling with systemic delivery of BM-derived mesenchymal stem cells (MSCs) into non-irradiated rats.

METHODS

Six-week-old Wistar rats were exposed to 3-week chronic hypoxia leading to pulmonary artery wall remodeling. Domiciliation of adhesive BM-derived CD45- CD73+ CD90+ MSCs was first studied after a single intravenous infusion of Indium-111-labeled MSCs followed by whole body scintigraphies and autoradiographies of different harvested organs. In a second set of experiments, enhanced-GFP labeling allowed to observe distribution at later times using sequential infusions during the 3-week hypoxia exposure.

RESULTS

A 30% pulmonary retention was observed by scintigraphies and no differences were observed in the global repartition between hypoxic and control groups. Intrapulmonary radioactivity repartition was homogenous in both groups, as shown by autoradiographies. BM-derived GFP-labeled MSCs were observed with a global repartition in liver, in spleen, in lung parenchyma and rarely in the adventitial layer of remodeled vessels. Furthermore this global repartition was not modified by hypoxia. Interestingly, these cells displayed in vivo bone marrow homing, proving a preservation of their viability and function. Bone marrow homing of GFP-labeled MSCs was increased in the hypoxic group.

CONCLUSION

Adhesive BM-derived CD45- CD73+ CD90+ MSCs are not integrated in the pulmonary arteries remodeled media after repeated intravenous infusions in contrast to previously described in systemic vascular remodeling or with endothelial progenitor cells infusions.

High-Resolution Imaging of Bone Precursor Cells Within the Intact Bone Marrow Cavity of Living Mice

Bone precursor cells (BPCs) play a critical role in bone maintenance and regeneration. Currently, no tool exists to study BPCs or other bone marrow cell types directly within their complex microenvironment. Here, we describe in vivo magnetic resonance imaging (MRI) of anatomical structures inside the medullary cavity of the mouse femur. We demonstrate that BPCs passively labeled with iron oxide-containing particles can be monitored by MRI within the intact bone marrow at an in-plane resolution of 43x25 microm. Anatomical detail provided by MRI is complemented by functional optical imaging of reporter gene expression. Single-cell dual iron oxide-reporter gene labeling has potential for combined cell tracking and cell biology studies. In summary, we describe a versatile platform suitable for studying the biology of many bone marrow cell types in living bone.

In vivo tracking of stem cells for clinical trials in cardiovascular disease

Various stem cells hold promise for the treatment of human cardiovascular disease. Regardless of stem cell origin, future clinical trials will require that the location and number of such cells be tracked in vivo, over long periods of time. The problem of tracking small numbers of cells in the body is a difficult one, and an optimal solution does not yet exist. We review the many contrast agents and detectors that have been proposed for stem cell tracking during clinical trials, define the characteristics of an ideal imaging technology, and suggest future directions for research.

The 2003 Nicolas Andry Award. Orthopaedic gene therapy

We review progress in the field of orthopaedic gene therapy since the concept of using gene transfer to address orthopaedic problems was initiated approximately 15 years ago. The original target, arthritis, has been the subject of two successful Phase I clinical trials, and additional human studies are pending in rheumatoid arthritis and osteoarthritis. The repair of damaged musculoskeletal tissues also has proved to be a fruitful area of research, and impressive enhancement of bone healing has been achieved in preclinical models. Rapid progress also is being made in the use of gene transfer to improve cartilage repair, ligament healing, and restoration of various additional tissues, including tendon and meniscus. Other applications include intervertebral disc degeneration, aseptic loosening, osteoporosis, genetic diseases, and orthopaedic tumors. Of these various orthopaedic targets of gene therapy, tissue repair is likely to make the earliest clinical impact because it can be achieved with existing technology. Tissue repair may become one of the earliest clinical successes for gene therapy as a whole. Orthopaedics promises to be a leading discipline for the use of human gene therapy.